Successful updates on three SP2's so far...
BUT a fourth unit is having major problems right now, though I just discovered that part of the reason may be due to a Type Cover 2 that has gone bad (I haven't used a type cover on this paticular SP2 for a long time and only plugged it in for the update today)?
I think the firmware update itself processed OK, but after the next boot when I tried to have it complete all the other Windows updates from today, it kept hanging during the update process. I'd force shut down, boot up and try again, etc. Sometimes it hangs in the WU window, but it had also hung during the purple "updating" screen forever. Then the next few times in a row when booting up, the system would just freeze after a few seconds in (touchscreen non-responsive, the mouse pointer only moves around but can't do anything). After I finally got it to continue running, I then noticed that the dreaded driver problem with "HID Sensor" in Device Manager had returned!
Also the screen sometimes just gets locked at max brightness, and the CPU sometimes gets locked at full speed and overheats for no reason. And SkyDrive had started taking a looong time to sync after booting, and I noticed that all my Libraries in Windows Explorer are messed up, can't even open them or open their properties! BTW I'd also gotten a couple of different error message pop-ups after boot-up. And now the Spyder screen calibration boot-up utility keeps popping up and complaining, though I probably just need to re-do it due to the surface display panel windows update...
Whew that was a mouthful.
This fourth SP2 has been getting more and more problems over the past few months anyways, so I guess it's time to finally request an extended warranty exchange. But local Microsoft Store just ran out of stock this past weekend, so I guess I'll do it by mail...
P.S. I've been wanting to get at least a fifth SP2 for the family, but have been holding back to see where the situation goes...